2 Establishing and maintaining geographical databases GIS data collection Data collection workflow Primary geographical data capture Secondary geographical data capture Obtaining data from external sources Geographical data standards Creating and maintaining geographical databases DBMS and GIS Geographical database types and functions Structuring geographical information Editing and data maintenance
Establishing and Maintaining Geographical Databases3 GIS data collection Data collection is one of the most time- consuming and expensive GIS tasks. Data capture costs can account for up to 85% of the cost of a GIS. In some cases, the cost of data collection and updating makes those on hardware and software insignificant (e.g. in cases of AM/FM).
Establishing and Maintaining Geographical Databases4 Analogue Maps Ground survey and historical records Remote sensor Images Editing and error correction Geocoding TabularVectorRaster Keyboard and computer media DigitiserScanner Computer media Data capture Editing and error correction Geocoding Storage and retrieval Data input process
Establishing and Maintaining Geographical Databases5 Data collection workflow Planning Editing / improvement Evaluation Digitising / transfer Preparation
Establishing and Maintaining Geographical Databases6 Primary geographical data collection Primary geographical data capture involves the direct measurement of objects. Raster data capture: mainly remote sensing. Resolution 0.5 m – 1 km. Vector data capture Surveying GPS
Establishing and Maintaining Geographical Databases8 Surveying Ground surveying uses measurements to determine the locations of objects.
Establishing and Maintaining Geographical Databases9 Traditional surveying
Establishing and Maintaining Geographical Databases10 Surveying with GPS
Establishing and Maintaining Geographical Databases11 Mobile mapping
Establishing and Maintaining Geographical Databases12 Secondary geographical data collection Raster data capture using scanners Vector data capture Manual digitising Vectorisation Photogrammetry
Establishing and Maintaining Geographical Databases13 Map scanning
Establishing and Maintaining Geographical Databases14 Image interpretation
Establishing and Maintaining Geographical Databases15 Obtaining data from external sources The best way to find geographical data is to search the Internet using one of the specialist geographical search engines. e.g. US NSDI Clearinghouse (http://www.fgdc.gov) e.g. MapWorld (China) (http://www.tianditu.cn) Others: ESRI Data: China Data Center, University of Michigan:
US NSDI Clearinghouse Establishing and Maintaining Geographical Databases16
MapWorld China Establishing and Maintaining Geographical Databases17
ESRI Data Establishing and Maintaining Geographical Databases18
China Data Centre, U-M Establishing and Maintaining Geographical Databases19
Establishing and Maintaining Geographical Databases20 Geographical data standards Geographical data can be encoded in many different ways (formats). No single format is appropriate for all tasks and applications. The most efficient way to translate data between systems is via a common intermediate file format. This intermediate file format often refers to a spatial data transfer standard.
Establishing and Maintaining Geographical Databases21 Data access Translation Direct read Source fileIntermediate fileDisplay in GIS application Source fileDisplay in GIS application
Data exchange using translators Establishing and Maintaining Geographical Databases22 Program 2 Program 6 Program 3 Program 1 Program 5 Program 4 T T T T T T T T T T T T = Translator T T
Data exchange using a standard Establishing and Maintaining Geographical Databases23 Program 2 Program 6 Program 3 Program 1 Program 5 Program 4 T T T T T T T T T T T T = Translator T T SDTS
Establishing and Maintaining Geographical Databases24 Creating and maintaining geographical databases A database is an integrated set of data on a particular subject. Advantages of the database approach: Collecting all data at a single location reduces redundancy and duplication. Maintenance costs decrease because of better organisation and decreased duplication. Applications become data independent so that multiple applications can use the same data. User knowledge can be transferred between applications more easily. Data sharing is facilitated. Security and standards for data and data access can be established and enforced.
Establishing and Maintaining Geographical Databases25 Database Management System (DBMS) A DBMS is a software application designed to organise the efficient and effective storage and access of data. Today, almost all large GIS use DBMS technology. Relational databases dominate GIS today, as they do in many other business areas. Several DBMS have now been extended so that they can support geographical data types and functions.
Establishing and Maintaining Geographical Databases26 The concepts of DBMS Data file 1 Data file 2 Data file 3 Application Program 1 Application Program 2 Output 1 Output 2 Sharing Data files among applications in the file processing environment
Establishing and Maintaining Geographical Databases27 The concept of DBMS (cont.) Data file 1 Data file 2 Data file 3 Application Program 1 Application Program 2 Output 1 Output 2 Sharing Data files among applications in a DBMS environment DBMS
Establishing and Maintaining Geographical Databases28 The view of database Client Sales Inven- tory Sup- pliers DBMS Date _________Client name _________ Address __________________________________ _________________________________________ QTYITEM UNIT PRICE TOTAL BALANCE Item _________ Supplier __________________________________ _________________________________________ MONTH UNITS SOLD UNITS RECEIVED UNITS ON HAND JAN FEB MARCH APRIL ACCOUNT EXECUTIVE VIEWINVENTORY MANAGEMENT VIEW Presentation of data base information using multiple views
Establishing and Maintaining Geographical Databases29 WhiteDouglas2Engineering CheungWai Ying1Environment KingAdam1Remote Sensing MitchellScott1GIS Last Name Field First Name Field Year Field Major Field Record 1 Record 2 Record 3 Record 4 Organisation of information as records in a data file Records
Establishing and Maintaining Geographical Databases30 Relational data structure Staff ID SchoolSubject Name CreditSubject ID GeographyPrinciple of GIS3GEOG GeographyRemote Sensing4GEOG SurveyingDTM3GMAT9532 Student ID Last Name First Name YearSchool WhiteDouglas2EE & C Sci CheungWai Ying1Biological Sci KingAdam1Geography School Name No. of A Staff No. of S Staff No. of Students Geography Physics Chemistry Staff ID Last Name First Name PositionSchool SmithJohnLecturerGeography PriceGeorgeA/ProfBiological Sci KingCraigProfessorMathematics Subject IDStudent ID GEOG GEOG GMAT GEOG GEOG GEOG Subject information Student information Staff information Registration information School information Organisation of a data base using the relational data model
Establishing and Maintaining Geographical Databases31 Relational join Staff ID SchoolSubject Name CreditSubject ID GeographyPrinciple of GIS3GEOG GeographyRemote Sensing4GEOG SurveyingDTM3GMAT9532 Student ID Last Name First Name YearSchool WhiteDouglas2EE & C Sci CheungWai Ying1Biological Sci KingAdam1Geography Subject IDStudent ID GEOG GEOG GMAT GEOG GEOG GEOG Subject information Student information Registration information SchoolSubject Name Student Last Name Subject ID GeographyPrinciple of GISWhiteGEOG9240 GeographyPrinciple of GISCheungGEOG9240 GeographyPrinciple of GISKingGEOG9240 Student First Name Douglas Wai Ying Adam Result of Join Operation The relational join operation
Establishing and Maintaining Geographical Databases Map IDArea (ha) Perimeter (m) Soil Type ID Soil Type ID NamepH 15Black soil6.5 21Brown soil6.0 25Red soil5.0 … Storage of GIS attribute information in a relational data base Use of DBMS for GIS
Establishing and Maintaining Geographical Databases33 Geographical database types and functions Methods to test spatial relations: Equals – are the geometries the same? Disjoint – do the geometries share a common point? Intersects – do the geometries intersect? Touches – do the geometries intersect at their boundaries? Crosses – do the geometries overlap? Within – is one geometry within another?
Establishing and Maintaining Geographical Databases34 Geographical database types and functions (Cont.) Methods to test spatial relations (cont.) : Contains – does one geometry completely contain another? Overlaps – do the geometries overlap (must be geometries of the same dimension)? Relate – are there intersections between the interior, boundary, or exterior of the geometries?
Establishing and Maintaining Geographical Databases35 Structuring geographical information Topologic creation Indexing A database index is a special representation of information about objects that improves searching.
Establishing and Maintaining Geographical Databases36 Metadata Metadata are data about data. Metadata are needed for: to enable the process of search and discovery over distributed archives; To assess the fitness of a dataset for a given use; To provide the information needed to handle the dataset effectively; and To provide useful information on the dataset’s contents.
Establishing and Maintaining Geographical Databases37 Metadata features Identification information Data quality information Spatial data organisation information Spatial reference information Entity and attribute information Distribution information Metadata reference information Citation information Time period information Contact information
Establishing and Maintaining Geographical Databases38 Geo-spatial metadata example
Establishing and Maintaining Geographical Databases39 Editing and maintenance Editing is the process of making changes to a geographical database by adding new objects or changing existing objects. This process is required to correct data input errors, Making geographical data more usable, and update geographical information.
Establishing and Maintaining Geographical Databases40 Errors in data input Paper maps are unstable so that the control points must be re-entered if the map is moved. The map may be stretched or shrunk in the interim of digitising making digitised points slightly off in their location. Errors on the map will be carried into GIS database. The level of error in GIS is directly related to the error level of the source maps.
Establishing and Maintaining Geographical Databases41 Cartographic errors Maps are meant to display information and do not always accurately record locational information. e.g. when a railway, stream and road all go through a narrow mountain pass, the pass may actually be depicted wider than its actual size.
Establishing and Maintaining Geographical Databases42 Edge matching errors Discrepancies across map boundaries can cause discrepancies in the total GIS data base. e.g. Roads or streams that do not meet exactly when two map sheets are placed next to each other.
Establishing and Maintaining Geographical Databases43 overshootundershoot spike Digitising errors User error causes overshoots, undershoots and spikes at intersection of lines.
Establishing and Maintaining Geographical Databases44 Error detection and editing Polygon not closedSliverGap Common errors in spatial data polygon not closed sliver gap attribute errors, etc.
Establishing and Maintaining Geographical Databases45 Examples of errors in spatial databases Dead end Leaking polygonInvalid polygon Slivers sliver Edge shiftAttribute errors
Establishing and Maintaining Geographical Databases47 Data maintenance and manipulation Format conversion Data reduction and generalization Edge matching Rectification and registration
Establishing and Maintaining Geographical Databases48 Data pre-processing Purpose: convert data sets for GIS database (data integration) Geographical data sets need to be converted to match: data type geo-referencing system data structure Products: coordinated set of thematic data layers
Establishing and Maintaining Geographical Databases49 Format conversion Data structure conversions Raster to raster: conversion between data formats, e.g. BSQ (Band Sequential), BIP (Band Interleaved by Pixel) and BIL (Band Interleaved) Raster to vector or vector to raster Data medium conversions
Establishing and Maintaining Geographical Databases50 Raster to raster conversion III AB BB Zoning Land cover Elevation BSQ (Band Sequential) File 1: Zoning:A, B, … File 2: Land cover:I, II, … File 3: Elevation:120, 140, … BIP (Band Interleaved by Pixel Line 1: A, I, 120; B, II, 140; … BIL (Band Interleaved by Line) A, B, … I, II, … 120, 140, … B, B, … … … Pixel 1Pixel 2 Line 1 Line 2
Establishing and Maintaining Geographical Databases51 Vector to raster conversion
Establishing and Maintaining Geographical Databases52 Data reduction and generalisation Data reduction Simplify data records Change scale Data generalisation Less precise representation Vector: less vertices and polygons Raster: resampling to larger pixel size
Establishing and Maintaining Geographical Databases53 Map generalisation Western Australia Northern Territory South Australia Queensland New South Wales Victoria Tasmania Western Australia Northern Territory South Australia Queensland New South Wales Tasmania Victoria Map generalisation
Establishing and Maintaining Geographical Databases54 Small area elimination MMU = 1 ha MMU = 9 ha *MMU = Minimum Mapping Unit
Establishing and Maintaining Geographical Databases55 Merging and establishing topology Clear minor errors and build spatial relationship Building from elemental points Creating topological structure Linking spatial and aspatial data sets
Establishing and Maintaining Geographical Databases56 Edge matching Original two map sheets Two sheets brought together showing discontinuities Derived single sheet with edges adjusted Joining map sheets Automated or manual procedures
Establishing and Maintaining Geographical Databases57 Rectification and registration Exact numerical approaches to rectification Transformation and map projection Approximation approaches to rectification Rubber sheeting Rotation, translation and scaling
Establishing and Maintaining Geographical Databases58 Map projection Azimuthal Point of contact Cylindrical Line of contact Conical Line of contact
Establishing and Maintaining Geographical Databases59 Map projection transformation MercatorMollweide
Establishing and Maintaining Geographical Databases60 Rubber sheeting A B C
Establishing and Maintaining Geographical Databases61 Summary Data input is the most costly and time consuming process in GIS. Data input include data capture, editing and geocoding processes. GIS is a data integration tool, so that spatial data needs to be properly structured, including the use of DBMS and creation of metadata. Before spatial data can be used, they need to be pre-processed for, e.g. error elimination, geographical registration, topology creation, data reduction and generalization, and coordinate transformation.